The volume on the WF-SP900 can't be adjusted

Try the following:

• Lift your finger, and then tap the tap sensor rather firmly.
  • If you do not put the headset's units on both of your ears, you can't adjust the volume, even if you tap the tap sensors.
• If the tap sensors are disabled, you can't adjust the volume. Use the following procedure to reactivate the tap sensors.
  1. Put the headset's units on both of your ears.
  2. If the Bluetooth® function is on, hold down the button on the left (L) unit for 2 seconds to turn off the Bluetooth function.
  3. Hold down the button on the right (R) unit for 4 seconds.
     • You can also reactivate the tap sensors when the headset's units are set in the charging case.